Process for making thiocyanogen derivatives



Patented May 19, 1953 PROCESS FORMAKING THIOOYANOGEN DERIVATIVES Harry1F.Pfann,:Pittsburgh,.Pa., assignor. to.Koppcrs Company, -IncPittsburgh,Pa a. n01.11

ration of Delaware No Drawing. Original application April=13,1948,Serial No. 20,840. Dividedgand;.this;application May. 6,1952; SerialNo.288,300.

18 Claims. 1

This invention relates to the manufacture of free thiocyanogen (SCN)2and derivatives prepared by the reaction of thiocyanogen with organiccompounds.

Heretofore thiocyanogen has been commonly made by treating eitherv ametal thiocyanate with elemental bromine, or by reacting a metalthiocyanate in solution with copper sulfate toform cupric-thiocyanatewhich in turn is decomposed to produce free thiocyanogen. While both ofthese processes are workable and yield free thiocyanogen, they aresubject to certain limitations, Thereaction of elemental bromine withthiocyanates is a costly process because of the expensive bromine whichis required. Thereaction of thiocyanates with copper sulfate yieldslarge quantities of the voluminous, insoluble precipitate of cuprousthiocyanate from which separation of the other desired reaction productsis somewhat difficult. Because of these and other considerations, itis'highly desirable to provide a more workable and less expensiveprocedure for the preparation of free thiocyanogen.

The primary object of the present inventionis to provide a process forthe production of free thiocyanogen from inexpensive raw materials andwith the production of a minimum of difficultly handled co-products.

Another object of this invention is to provide a process for theproduction of free thiocyanogen in such a medium that is .may be readilyreacted with Qrganiccompounds to make thiocyanogen derivatives.

A further object of the invention is to provide a cyclic process for'theproduction of freethiocyanogen in which process no co-products orbyproducts are formed which are not easily removed from the reactionmedium in a simple cyclic system.

Ihave'now discovered that thiocyanogen may be produced-by using hydrogenperoxide as'an oxidizing agent to react upon thiocyanic acid or uponsolutions of thiocyanates in acid medium. The reaction is presumed toproceed according to the following equation:

Accordin ly, thiocyanic acid dissolved in a suitable, reaction mediumsuch as ethyl, alcohol may be treated with hydrogen peroxidetoform freevth-iocyanogen. and 1 water. The reaction. medium should be acidic.

Alternatively, a solution of a metal thiocyan-ate dissolved;ingarsolvent, may be made :acid with a strongxacidcsuch as sulfuric 1 orphosphoricacid,

.2 andthereupon .treated, with hydrogen peroxide as in the foregoingprocedure.

.In either-of. the above processe th Or ani compound .to bereacted',Withthe free thiocyanogenmay .beadded prior to the introduction of thehydro nip roxidetor, thesolution of free thiocyanogen .in the solventmaybe added to the organicpompound which is to be thiocyanated.,Eor,most., 10mme1:cia1 processes, it is preferredto prepare the.solutionof alkali thiocyanate and reactant organic compound in .thesolvent, and .then a.1.d at .a controlledrate the hydrogenperoxide whichis.to efiect the liberationofvthe freethiocvanogen. The rateoi oxidationof the thiocyanic acid by the hydrogen peroxide should be such as topermit simultaneous reaction ofatheifreesthiocyanogen without the.accumulation. of appreciable quantities obit. :Such-controlof.,thereaction will lead to the, formation. ;of t,hiocyano derivatives.with a minimum .of=undesirable-hyeproducts such ,as perthiocyanic acidand related compounds.

As a reaction medium there may be used any non-reactive liquid which isboth a solvent for the thiocyan-ic-acid; or for-thealkali thiocyanate ifit --isused, and i also a solvent :for hydrogen peroxide-and the organic-compound"to be reacted -upon. Examples of solvents which'are suitableinclude --meth-yl alcohol, ethyl alcohol,isopropyLalcohoh.and..tert-butylalcohol. ,Acetic acid may also .be-used,as may-the lower fatty acid esters-such as ethyl acetate? Etherderivativessuchrasdioxane and the methylether ,of ethylene: glycol orthereth-yl ether. of. diethylene glycol are likewise suitable.

-As an oxidizing agent, itisdesirableto ,use hydrogen peroxide'ofbetween. 30 and. 90% purity in ordcrto minimize the quantities handledand tominimize dilutionof thereactionmedium. .Hydrogen peroxide. ofhigher concentration is efiective. butiat. the present. time it, isrelatively more expensive .than the lower concentration products.Hydrogen peroxide of concentrations lower than 3.0% is workable, butinvolves the undesirable factor of great dilution of thereaction=m-i-xtures.

Suitable acidsfor reaction'with'the alkali-thiccyanates to form-t-hiocyanic acid include sulfuric and phosphoric acid; Nitric acidmaybe usedunder-certain conditions, but it" is generally desiredto,avoid an acid possessing oxidizing properties when. working in amedium containingreactive organic compounds such as ethyl'alcohol. Thehalogen acids such as hydrochloric and :hydmbromic acid are. normallytobe avoided 3 because of their reactivity with hydrogen peroxide.

Control of the reaction temperature is important. If the temperature ispermitted to rise appreciably above 50 C}, the rate of polymerization offree thiocyanogen to perthiocyanic acid becomes excessive. Attemperatures below C. the rate of reaction of hydrogen peroxide withthiocyanic acid is too low for practical purposes. Preferredtemperatures are between C. and 30 C.

The following reactive organic compounds can be treated with freethiocyanogen in order to prepare thiocyanogen derivatives: aromaticamines such as aniline and its homologs, including ethyl aniline,diethyl aniline, butyl aniline, dibutyl aniline, diphenyl amine, andsubstituted anilines such as the chloro and nitro anilines; phenolderivatives such as the nitro phenols, chlorophenols, and ortho-cresol;hydroxyphenols such as resorcinol, catechol, pyrogallol, andphloroglucinol; unsaturated organic compounds such as butadiene,isobutylene, vinylcyclohexene, styrene monomer, dicyclopentadiene, allylchloride, allyl alcohol, drying oils and their fatty acids, and otherolefinic compounds. In the specification and claims the above listedcompounds will be referred to as thiocyanogen acceptors.

Illustrative of the processes which may be used to carry out the presentreactions are the following examples, which examples are given by way ofillustration but are in no sense to be considered limiting as to thescope of the present invention. In the following examples all quantitiesrepresent parts by weight.

Example I To produce a solution of free thiocyanogen in a mixture ofalcohol and water, the following reactants were added in the indicatedorder to a suitable vessel equipped for agitation and cool mg.

Water 150 Methanol 100 Sulfuric acid, concentrated 25 Sodiumthiocyanate-0.3 mole 25 Hydrogen peroxide, 30%0.27 mole 30 To thesolution of sodium thiocyanate in an alcohol-water solvent the sulfuricacid was gradually added with simultaneous cooling and agitation. Theresultant solution of thiocyanic acid was cooled to 10 C. and thehydrogen peroxide was then gradually added. The free thiocyanic acid wasobtained as a clear orange-colored solution in alcohol-water solvent.Preferably the free thiocyanic acid may be used for reaction with athiocyanogen acceptor such as described in Example IV below. In order tominimize the polymerization of the thiocyanic acid to perthiocyanicacid, the temperature of the reaction mixture should be held atapproximately 0 C. until it is used.

Example II An aqueous solution of thiocyanic acid was mixed with ethylether so as to take up the thiocyanic acid in ether. The ether wasseparated from the aqueous phase and added to an amount of anhydrousethanol equivalent to one-third the volume of ether solution. To theether thiocyanic acid-ethanol solution was added a slight excess of 30%hydrogen peroxide which reacted with the thiocyanic acid in accordancewith the equation above.

This solution of free thiocyanogen, without the inorganic salts or acidswhich are present in solutions of free thiocyanogen prepared byconventional methods, was taken for reaction with a thiocyanogenacceptor as described in Example IV below.

Example III For the production of thiocyano-meta-toluidine, thefollowing reactants were charged to a kettle in the order shown:

Methanol 500 Sodium thiocyanate 48.5 Meta-toluidine 26.7 Sulfuric acid,conc. 51.0 Acetic acid, glacial 50.0 Hydrogen peroxide 68.0 Methanol74.0

The addition of the sulfuric acid caused the precipitation of themeta-toluidine sulfate. This formed a heavy slurry which was diluted andpartially dissolved with acetic acid. Over a period of 2 to 3 hoursthere was added, in increments, the hydrogen peroxide which had beenmixed with an equal volume of methanol. The temperature of the reactionmixture was maintained at 18-21 C. during the addition of most of theperoxide, and was finally permitted to rise to 30 C. at the end of thereaction. The color of the mixture which had remained light during theaddition of most of the hydrogen peroxide, turned quite dark at the endwhen an excess of free thiocyanogen was present.

The reaction mixture was poured into a large volume of water madealkaline by the addition of sodium hydroxide, and the alkaline mixturewas extracted once with benzene to recover the thiocyano-meta-toluidine. The benzene solution, after being treated with anadsorbent activated carbon such as Darco, was filtered, and the benzeneremoved by distillation at reduced pressure to leave a residue of crudethiocyano-metatoluidine amounting to 74% of theory. After severalrecrystallizations from ethanol-water mixtures a white crystallineproduct was obtained having a melting point range of 78-80 C.

Example IV For the preparation of the thiocyanogen addition products ofolefinic hydrocarbons and other thiocyanogen acceptors of limitedsolubility in polar solvents, it is desirable to carry out the reactionin an ether solution. For such cases solutions of free thiocyanogen, asprepared by Example II, are used as the source of thiocyanogen. Thus, toa solution of higher molecular weight olefin such as decene-l dissolvedin carbon tetrachloride there is slowly added a solution of freethiocyanogen in ether. After allowing sufficient time for the reactionof the thiocyanogen with the olefin, the reaction mixture is filteredfor removal of any perthiocyanic which may have formed. Thedithiocyanodecane is then recovered by removal of the solvent bydistilling at reduced pressure.

This general technique may be applied with equal advantage to solutionsof thiocyanogen acceptors in hexane, decahydronaphthalene, cyclohexane,ethylene dichloride, and similar classes of compounds in which inorganicthiocyanates are insoluble.

This application is a division of application Serial Number 20,840,filed April 13, 1948.

The preferred form of the invention having been thus described, what isclaimed as new is:

1. In a process for preparing a thiocyanogen derivative of athiocyanogen acceptor selected from the class consisting of aromaticamines, phenols and olefinic compounds the steps of bringing thiocyanicacid, hydrogen peroxide, and said thiocyanogen acceptor together in amutual solvent at a temperature between about '0 and 50 C. andrecovering the thiocyanogen derivative therefrom.

2. The process of claim 1 in which the mutual solvent comprises analcohol.

3. The process of claim 1 in which the thiocyanic acid is formed in situfrom a mineral acid and a salt of thiocyanic acid.

4. The process of claim 3 in which a mutual solvent comprises a mixtureof methanol and acetic acid.

5. The process of claim 1 in which the thiocyanic acid is extracted froman aqueous solution of thiocyanic acid into a solvent component of saidmutual solvent.

6. The process of claim 5 in which said solvent component is diethylether.

'7. The process of claim 6 in which the mutual solvent also containsethanol.

8. The process of claim 1 in which the thiocyanogen acceptor is anaromatic amine.

9. The process of claim 1 in which the thiocyanogen acceptor is aphenol.

10. The process of claim 1 in which the thiocyanogen acceptor is anolefine.

11. In a process for preparing a thiocyanogen derivative of thiocyanogenacceptors selected from the class consisting of aromatic amines,phenols, and olefins the steps of bringing together a salt of thiocyanicacid, said thiocyanogen acceptor, a mineral acid in proportion to freethe thiocyanic acid from its salt and, when said thiocyanogen acceptoris an aromatic amine, in proportion to unite with the amine to form themineral acid salt thereof, and hydrogen peroxide in a mutual solvent ata temperature between about 0 and C., and recovering said thiocyanogenderivative from the reaction mixture.

12. The process of claim 11 in which the mutual solvent comprisesmethanol and acetic acid and the mineral acid is sulfuric acid.

13. The process of claim 11 in which the thiocyanogen acceptor is aphenol.

14. The process of claim 13 in which the mutual solvent comprisesmethanol and acetic acid and the mineral acid is sulfuric acid.

15. The process of claim 11 in which the thiocyanogen acceptor is anolefine.

16. The process of claim 15 in which the mutual solvent comprisesmethanol and acetic acid and the mineral acid is sulfuric acid.

17. The process of claim 11, in which the thiocyanogen acceptor is anaromatic amine.

18. The process of claim 17 in which the mutual solvent comprisesmethanol and acetic acid and the mineral acid is sulfuric acid.

HARRY F. PFANN.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,212,175 Clayton et a1. Aug. 20, 1940 2,342,448 Bousquet Feb.22, 1944 2,395,453 Bruson Feb. 26, 1946 2,395,455 Bruson Feb. 26, 1946

1. IN A PROCESS FOR PREPARING A THIOCYANOGEN DERIVATIVE OF ATHIOCYANOGEN ACCEPTOR SELECTED FROM THE CLASS CONSISTING OF AROMATICAMINES, PHONELS AND OLEFINIC COMPOUNDS THE STEPS OF BRINGING THIOCYANICACID, HYDROGEN PEROXIDE, AND SAID THIOCYANOGEN ACCEPTOR TOGETHER IN AMUTUAL SOLVENT AT A TEMPERATURE BETWEEN ABOUT 0 AND 50* C. ANDRECOVERING THE THIOCYANOGEN DERIVATIVE THEREFROM.